The present application relates to an apparatus and method for calibrating surround-view camera systems, for example, to an apparatus and method for calibrating vehicular surround-view camera systems.
Surround-view camera systems produce a bird's-eye view of the scene around a vehicle using one or more cameras. This bird's-eye view aids the driver in maneuvering the vehicle. In general, the surround-view camera calibration process “stitches” the adjacent images from adjacent cameras together so that common elements in the separate images directly overlap with each other to provide a desired view.
The calibration stage for these surround-view camera systems typically requires associating marker locations, seen in an image taken by each camera, with the actual location of these markers on the ground. For this purpose, the markers need to be placed at precise locations on the ground (e.g., precise (x, y) position of the marker on the ground). However, conventional methods of measuring the actual ground location of the markers involve long and painstaking labor, and are often prone to human error, which can lead to less accurate calibration results. In particular, this room for human error during the calibration process becomes greater as the size of the vehicle becomes bigger (e.g., trailer, bus, etc.).
In view of the foregoing, it is an objective of the present invention to provide new apparatuses and methods that render surround-view camera calibration processes less time-consuming, less labor-intensive, less prone to human error, and easier to set up.
In accordance with one aspect of the present invention, a calibration apparatus is provided for a surround-view camera system having a plurality of cameras mounted to an object. The calibration apparatus includes a plurality of markers that are arbitrarily placed in an area around the object and configured to measure a plurality of distances between one another. The calibration apparatus includes a controller which is configured to visually identify two or more of the markers from at least one image of the cameras. The controller generates calibration information based on the measured plurality of distances and the visually identified markers. The controller is preferably mounted on the object, but may be located remotely from the object.
Preferably, the controller visually identifies two or more markers via a visually distinctive characteristic on a corresponding marker. The visually distinctive characteristic may be uniquely associated with the corresponding marker and be, for example, a shape, a color, a texture, a size, a pattern and/or a reflectivity. The markers may communicate with other markers or the controller, and may include a unique identification code such that the other markers or the controller is able to identify which marker is communicating. A hierarchy may exist for the plurality of markers, for example, where a marker functions as a master marker with respect to the rest of markers which are slave markers. The master marker may perform a data cleanup process on the received measured distances before transmitting to the controller.
In accordance with another aspect of the present invention, a marker is provided, which is to be arbitrarily placed in an area to measure a distance between itself and another marker that is also arbitrarily placed in the area. The marker includes a rangefinder that is capable of measuring a distance between the marker and another marker. The marker further includes a visually distinctive characteristic thereon via which the marker is visually identified.
Preferably, the center of the visually distinctive characteristic coincides with the center of the marker. The marker or a portion of the marker may be capable of being pivotably or tiltably adjusted such that the visually distinctive characteristic is readily observable from an observing direction. The marker preferably includes a transmitter and a receiver, thus it is capable of communicating the measured distance with another marker or a controller via the transmitter and/or the receiver. The marker's body is preferably of radially symmetrical construction. The marker's body may include at least one reflective surface that reflects a light pulse from another marker. The body may include a stepped portion such that the body provides at least two reflective surfaces having different radii relative to a center line of the body. Preferably, the differential value of the different radii is uniquely associated with the marker such that the differential value is used to identify the marker.
In accordance with another aspect of the present invention, a method is provided for calibrating a surround-view camera system having a plurality of cameras mounted to an object. The method comprises arbitrarily placing a plurality of markers in the area around the object, having the plurality of markers measure distances between one another, visually identifying two or more of the plurality of markers from at least one image of the plurality of cameras; and generating calibration information based on the measured plurality of distances and the visually identified markers from the at least one image of the plurality of cameras.
In accordance with another aspect of the present invention, an object equipped with a surround-view camera system having a plurality of cameras mounted to the object is provided. The surround-view camera system is calibrated via a calibration apparatus provided in the present application. The object is preferably a vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.